Life support for patients with compromised respiratory function is commonly maintained by periodic introduction and extraction of a respiratory gas by mechanical means, such as a ventilator, through a tube inserted into the trachea of a patient. Introduction of the respiratory gas at a positive pressure causes the gas to move into and inflate the patient's lungs. After a predetermined time interval, the ventilator reduces the gas pressure and the patient's lungs deflate, causing the respiratory gas to be passively exhaled. Alternately pressurizing and depressurizing the patient's lungs with the respiratory gas, generally referred to as a ventilatory cycle, introduces oxygen into the lungs and removes carbon dioxide from the lungs which is necessary to keep the patient alive.
During the ventilatory cycle, various components of the ventilator are exposed to patient exhaled gases and can therefore be contaminated thereby. This poses a risk of cross-infection between successive patients treated with the ventilator. Given the extensive network of valves, tubes, and various chambers that are a part of a ventilator system, the challenge of sterilizing contaminated areas is daunting.
Although the risk of cross-infection is one problem to be overcome, it should be understood that other problems bear directly on the pneumatic performance of a ventilator. For example, rapid response to patient demand is highly desirable. Additionally, ventilators that provide gases for inspiration directly from a wall supply or a compressor must continuously feed the patient airway with gas from the supply source. This places a heavy demand on the gas source which can result in rapid depletion of gas supply. Worse yet, the demands of a patient or ventilator may exceed the capabilities of the supply sources.